1. Field of the Invention
This invention relates generally to grinding apparatus, and more particularly to a grinding machine provided with an apparatus for changing a feed rate of a grinding wheel relative to a workpiece just before the grinding wheel comes into contact with the workpiece.
2. Description of the Prior Art
In the past, for the purpose of detecting the contacting of a grinding wheel with a workpiece, conventional feed rate-changing devices utilize a change of input current of a grinding wheel-driving motor caused by the contacting of the grinding wheel with the workpiece, a change of moment of the rotating grinding wheel, or a vibration or a noise caused by the contacting of the grinding wheel with the workpiece. While somewhat satisfactory, the feed rate changing devices using such detecting methods cannot, however, change the feed rate of the grinding wheel just before or at the moment of contact of the grinding wheel with the workpiece.
Another previous method for detecting the contacting of the grinding wheel with the workpiece utilizes a conductive circuit formed by the contact between a grinding machine and a conductive grinding wheel. Again, while somewhat satisfactory, this method suffers from the drawback that a non-conductive grinding wheel cannot be utilized.